What is this 'Comment'-like pop-up feature in Excel ?

I've just come across a feature in Excel which I've never seen before. When I click on a cell it displays as a pop-up box with comment-friendly text inside. The pop-up can be dragged around the sheet but I can't find a way of editing the text or deleting it completely. If I click off the box, it hides.

It's not a Comment because I can insert and edit one of those in the same cell as the pop-up.

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Introduction
This Article briefly covers methods of calculating the NPV and IRR variants in Excel as well as the limitations in calculating and interpreting IRR results.
Paraphrasing Richard Shockley, author of my favourite finance reference tex…

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